“Tilt-up” is a construction technique commonly used in constructing industrial-scale buildings such as warehouses. In tilt-up construction, an area of land is generally cleared of organic debris and other obstructions (e.g. boulders), and brought down to suitable elevation and grade. The land is checked to ensure that it is capable of supporting a building foundation. Footings lying around the perimeter of the area of land are poured. Wet concrete is then poured over the ground and allowed to set and form a concrete slab. The concrete slab forms the flooring of the building. To prevent surfaces bonding to the concrete slab, the concrete slab is sprayed with a chemically reactive bond breaker. Concrete elements such as walls (e.g. exterior walls) are then formed horizontally on top of the concrete slab by pouring wet concrete into a pre-defined area defined by a wood formwork. The wet concrete sets to form the concrete element. The wood formwork is removed, and the concrete element is then tilted to an upright position from a horizontal position and positioned at the perimeter of the concrete slab.
Exterior walls made for tilt-up construction generally comprise: (i) an exterior layer called a fascia wythe; (ii) an interior layer called a structural wythe; and (iii) insulating material therebetween. To form an exterior wall, welded wire mesh is laid within the pre-defined area defined by the wood formwork, and a first layer of wet concrete is poured over the welded wire mesh. This first layer of wet concrete sets and forms the fascia wythe. Before the first layer of wet concrete sets, insulating material is positioned over the first layer of wet concrete and coupled to the first layer of wet concrete by methods known in the art. The insulating material is generally a non-weight bearing insulating material (e.g. extruded polystyrene insulation). Once the first layer of wet concrete has set, reinforcing bars are laid out over the insulating material, and a second layer of wet concrete is poured over the reinforcing bars and insulating material. The second layer of wet concrete is coupled to the insulating material by methods known in the art and sets to form the structural wythe. A construction crane may then be used to manoeuvre the exterior wall to its desired upright location and position.
Previously, building energy codes pertaining to industrial buildings did not require an exterior wall to be insulated. As such, it was common practice to have only the structural wythe as the exterior wall (i.e. no insulating material and no fascia wythe), and to mount fixtures directly onto the structural wythe since the structural wythe was reinforced with reinforcing bar and therefore had the structural properties to provide a weight-bearing surface for fixtures. Fixtures include, but are not limited to, door frames, window frames venting grills or other building components. However, it is now common place for new industrial buildings, including “tilt-up” concrete buildings, to be required to meet certain energy efficiency standards. Under these new building energy codes, exterior walls must be insulated. As such, new building energy codes essentially require that a fascia wythe and a structural wythe of an exterior wall be separated by insulating material or a thermal break at all locations along the two layers of wythes. Such an exterior wall is exemplified in FIG. 1(a), which shows a structural wythe 110 and a fascia wythe 120 of an exterior wall 100 separated by insulating material 130.
Generally, a fixture (e.g. a door frame) is mounted onto the exterior wall such that the width of the fixture covers the insulating material that extends to the perimeter of the exterior wall, thereby also acting as a barrier that reduces the loss of thermal energy where the insulating material meets the perimeter of the exterior wall. However, the insulating material is not weight-bearing, and direct mounting of a fixture onto the insulating material may result in structural failure over time. One option is to modify the shape of the insulating material and the shape of the structural wythe such that only a narrow rib of insulating material extends towards the perimeter of the exterior wall. In this arrangement, and referring to FIG. 1(b), a fixture 140 may be mounted mainly to the structural wythe 110 while still covering surface 130a of the insulating material 130. However, because the fixture 140 still overlaps at least a portion of the non-weight-bearing insulating material 130 (i.e. over insulating material surface 130a), structural failure where the fixture overlaps with the non-weight-bearing insulating material may still occur over time.
Another option is to position a piece of wood 150 between insulating material 130 and the perimeter of the exterior wall as shown in FIG. 1(c). The wood 150 acts as a heat loss barrier and also provides a mounting and weight-bearing surface for fixture 140. However, wood and concrete expand and contract at different rates, and the combination may eventually lead to mechanical failure. In addition, moisture can access the wood, and can lead to wood rot over time.